This invention relates generally to frequency conversion of electrical signals, and more particularly the invention relates to sideband suppression in frequency conversion.
Audio signals and other low frequency signals must be up converted to higher frequencies for wireless transmission. Typically, a mixer driven by a high frequency local oscillator (LO) is used to step up the low frequency (IF) signal. A mixer generates two sidebands, FLO+FIF and FLOxe2x88x92FIF. Before transmitting the output from the mixer, one of the sidebands must be suppressed, otherwise the two sidebands can interfere and result in garbled information.
Heretofore, sideband suppression has been achieved by use of active circuit components and buffers and filters which consume power. Further, output signals typically are currents and not voltages. Such techniques are not very efficient, especially in CMOS circuit technology.
In accordance with the invention, a mixer is provided which is compatible with CMOS technology and achieves voltage mode sideband suppression.
Briefly, a mixer in accordance with the invention uses two mixer circuits operating on in-phase and quadrature phase low frequency (IF) sidebands with the two mixers driven by local oscillators having the same frequency but phase offset signals. The outputs of the two mixers are combined to eliminate one of the sidebands as determined by the phase relationships of the IF input signals to the two mixers.
More particularly, by introducing phase shift, a sign reversal is realized in one of the sidebands from one of the mixers. When the outputs of the two mixers are combined, the sign reversal leads to cancellation of one sideband.
The invention and objects and pictures thereof will be more readily apparent from the following detailed description and appended claims when taken with the drawing.